It has been previous practice in railway vehicle braking systems designed for low temperature operations to provide means for maintaining a virtually continuous light rubbing brake application between the shoes of tread brakes and braked wheels of a vehicle during adverse conditions of snow or ice. Such light braking, while not producing an appreciable retarding effect on the train, generates friction and heat sufficient to reduce build-up of ice on the wheel treads and therefore to ensure more predictable service or emergency braking performance. One shortcoming of such a facility is that once actuated, normal braking during such a brake operation may result in wear on the tread brake shoes which is so excessive as to eventually prevent a subsequent full and proper brake operation. In co-pending, commonly assigned U.S. patent application Ser. No. 06/134,764 filed on Mar. 28, 1980, now U.S. Pat. No. 4,364,610 there is provided a railway vehicle braking system including "snow brake" control means for maintaining a light brake application during normal traction or coasting in order to reduce icing of wheels of a vehicle, and including override means operable from time-to-time without conscious action by a driver to override said "snow brake" means to permit complete, but temporary, brake release. The duration of this automatic, intermittent full release of the brakes is such as to afford the automatic slack adjusters provided in the system sufficient opportunity to make whatever adjustment is necessary to accommodate any detected excess of slack. Thus, by virtue of the override means, the automatic slack adjusters provided in the system are operated sufficiently frequently, and in a manner consistent with their proper operation.